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    <script>
        // alert(1 + '10');
        // alert(true + false); // 1 + 0
        alert(null - 10); // -10
        /*
            隐式类型转换：
                参考ECMAScript
                
               英文 http://www.ecma-international.org/ecma-262/5.1/# 
               
               中文 http://www.fengfly.com/document/ECMAScript5.1/


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